The present invention relates to horn attachment arms for bonding apparatuses.
A semiconductor manufacturing process includes various steps such as die bonding with which a semiconductor die is mounted to a circuit board, and wire bonding with which an electrode of the semiconductor die mounted to the circuit board by the die bonding is connected to an electrode of the circuit board with a wire. In such die bonding and wire bonding, a die bonding apparatus and a wire bonding apparatus are used respectively. Such an apparatus is each provided with a bonding tool such as a collet that pressure-bonds the semiconductor die to the circuit board or a capillary that pressure-bonds the connection wire threaded there threw to the respective electrodes. The bonding tool is attached to a tip end of an ultrasonic horn. The tip end is driven up and down by a driving motor, and an ultrasonic transducer that vibrates the bonding tool when bonding is attached to a rear end of the ultrasonic horn.
As an example, Japanese Patent Application Unexamined Publication Disclosure No. H05-82577 proposes a structure of a wire bonding apparatus in which an ultrasonic horn attached with a capillary at its tip end is supported rotatably about a rotating shaft along with a yoke of a driving motor, and vibrating the yoke of the driving motor causes the ultrasonic horn to rotate about the rotating shaft in forward and backward directions, thereby driving the tip end of the ultrasonic horn in a Z direction, which is an upward-downward direction.
Japanese Patent Application Unexamined Publication Disclosure No. 2003-258021 proposes a structure of a wire bonding apparatus configured such that, a driving motor is provided at one end of a supporting frame rotatable about a rotating shaft, and rotating the supporting frame by the driving motor causes the tip end of the ultrasonic horn that is attached to the other end of the supporting frame to be driven in the Z direction, which is an upward-downward direction.
In addition, because a workpiece such as the circuit board or the semiconductor die is required to be heated when bonding depending on the type of the workpiece, a bonding stage on which a circuit board is fixed by vacuum suction is provided with a heating unit such as an electrical heater. Accordingly, the radiated heat generated from the circuit board that has been heated by the heater when bonding is transmitted to the ultrasonic horn, resulting in an increase of the temperature of the ultrasonic horn (for example, see Japanese Patent Application Unexamined Publication Disclosure Nos. 2000-332050 and 2000-164624). Because the capillary is attached to a tip end portion of the horn that is cantilevered, a varying temperature of the ultrasonic horn causes positional variation of the capillary.
In view of the above problem, Japanese Patent Application Unexamined Publication Disclosure No. 2000-332050 proposes providing a shielding plate and an air cooling nozzle in order to avoid the heat radiated from a heater of a bonding stage. Further, Japanese Patent Application Unexamined Publication Disclosure No. 2000-164624 proposes a method of cooling an ultrasonic horn by providing a path for coolant air to cool the ultrasonic horn.
According to the wire bonding apparatus disclosed by any of Japanese Patent Application Unexamined Publication Disclosure Nos. H05-82577 and 2003-258021, the tip end of the capillary must be vertical to the workpiece in a state in which the capillary attached to the tip end of the ultrasonic horn is brought into contact with the workpiece. Consequently, a rotational center of the ultrasonic horn or the supporting frame is required to be as high as the tip end of the capillary in the contact state. Thus, the size of the circuit board that can be bonded is limited by the length of the ultrasonic horn.
Despite such a limitation, the recent trend of increasing in size of the circuit board demands the capability of bonding to a larger workpiece. However, the ultrasonic horn is formed by a metal so as to exhibit a predetermined standing wave and a predetermined exciting force, because the ultrasonic horn is formed as an arm from the rotational center, and at the same time, serves to pressure bond the wire by exciting the capillary at the tip end using the ultrasonic transducer attached to the horn. Accordingly, increasing the length of the ultrasonic horn in order to adopt the bonding to a larger workpiece adversely increases the weight of the horn and a moment of inertia of rotation of the ultrasonic horn about the rotational center, resulting in a problem that it is difficult to drive at a high speed.
Further, according to the method of cooling the ultrasonic horn by air as disclosed in Japanese Patent Application Unexamined Publication Disclosure No. 2000-332050 or 2000-164624, a temperature variation of about two to three degrees Celsius can be caused in the ultrasonic horn depending on how the coolant air is blown onto the ultrasonic horn. Accordingly, it is difficult to prevent deterioration in the bonding quality due to the positional displacement of the ultrasonic horn.
Moreover, the ultrasonic horn is formed by a metal having high thermal expansion. Accordingly, increasing the length of the ultrasonic horn to adopt a larger circuit board also adversely increases the positional variation due to the varying temperature, resulting in a problem that the bonding accuracy decreases.